Chain structure comparison of two impact polypropylene copolymers with good balance between stiffness and flowability

Abstract

Impact polypropylene shows good toughness at low temperatures and has different types, such as high stiffness, high toughness, and high flowability, allowing it to be applied in various scenarios. Two impact polypropylene alloys (F18 and F15) with high stiffness (1828 and 1498 MPa of flexural modulus) and high flowability (54.6 and 61.0 g/10 min of melt flow rate) are separated into nine fractions at specific temperatures using preparative temperature rising elution fractionation (P-TREF). The total content eluted at high temperatures (125 − 140 °C) in F18 is 31.13 wt%, which is 1.2 times higher than 14.26 wt% in F15. Such highly crystalline PP homopolymers provide enough stiffness in the matrix, thus, sample F18 has better stiffness. Two resins both have high flowability. F18 has 9.95 % low molecular weight components (<2 × 10⁴ g/mol) and 4.65 % high molecular weight components (>10⁶ g/mol). The composition of F15 includes 12.72 % low molecular weight components and 2.65 % high molecular weight components. The improved flowability of F15 can be attributed to its higher proportion of low molecular weight components and lower proportion of high molecular weight components. In short, sample F18 has a good stiffness-flowability balance. The toughness and morphological characteristics were also discussed.